EPSP Synthase Inhibitors

HRAC Group: G

WSSA: 9

Glycines (glyphosate) are herbicides that inhibit 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase, a key enzyme in the shikimic acid pathway, which is involved in the synthesis of the aromatic amino acids. EPSP inhibition leads to depletion of the aromatic amino acids tryptophan, tyrosine, and phenylalanine that are needed for protein synthesis. Glyphosate resistant crops with an alternative EPSP enzyme have been developed that allow using glyphosate on these crops with no crop injury. Glyphosate is a relatively nonselective postemergent herbicide that is inactive in the soil because of high soil adsorption. The EPSP Inhibitor herbicides are readily absorbed through plant foliage and translocated in the phloem to the growing points.

Injury symptoms

Glycine symptom intensity varies depending on the rate of application, amount of herbicide off-target drift, the plant species receptor involved, and environmental conditions. Injury symptoms are not apparent until 3 to 7 days after treatment and usually develop more slowly in woody plants. Injury symptoms also develop more slowly under cooler weather.  Symptoms include leaf shape distortion, interveinal chlorosis, stunting, crinkling, cupping of developing leaves, and slow death in annual plants. Grasses exposed to glyphosate drift may exhibit a chlorotic band across the leaves in the whorl of the plant. Glyphosate drift to wheat plants at the heading stage of growth can result in white heads and stems above the flag leaf, while the rest of the plant remains green. Woody perennial usually are less sensitive to glyphosate than annual plants. Growth of sensitive trees, shrubs, and vines usually slows or stops one to two weeks after exposure (this period will fluctuate depending on the maturity of the tree concerned, plant species, rate, and environmental conditions). Leaves of trees and vines become chlorotic 3 to 7 days after exposure, and margins of new leaves become necrotic. Where there is high herbicide uptake, the meristematic tip on the stem will die followed by stem dieback. The buds below the dead parts usually grow after a period of time forming new growth that is generally stunted or distorted. After a period of time the plant will resume growth.

Chemistry Group and Common Names of EPSP Inhibitors
Used in the United States